The purpose of this core is to consolidate key personnel and equipment to provide a centralized facility to[unreadable] enhance collaborative and multidisciplinary investigations into the multiple mechanisms of osteoporosis in[unreadable] old age. Core C will perform six labor-intensive and highly specialized procedures in a cost- and timeefficient[unreadable] manner to facilitate the examination of the changes in bone cells, architecture, mass, and strength[unreadable] that accompany old age. Aim 1. Prepare undecalcified, plastic-embedded, tetracycline-labeled bone[unreadable] sections to supply the project leaders with the materials necessary for a quantitative static and dynamic[unreadable] histological analysis of axial (lumbar vertebrae) and appendicular (distal femoral) bone. The core will also[unreadable] prepare sections by in-situ nick-end labeling to determine the prevalence of osteoblast and osteocyte[unreadable] apoptosis. Aim 2. Obtain frozen sections of undecalcified bone using a dedicated cryostat and tape-transfer[unreadable] system to facilitate quantification of p-galactosidase activity, immunostaining of targeted cells in transgenic[unreadable] animals, and recognition of green fluorescent protein at the same time as tetracycline labels. These needs[unreadable] of the program cannot be accomplished with standard plastic-embedded or decalcified, paraffin-embedded[unreadable] sections. The core will also be responsible for freezer storage of these specimens. Aim 3. Perform micro-CT[unreadable] measurements using a unique horizontal imaging system to acquire images comparable to those obtained[unreadable] by longitudinal sections for bone histology. In a customized specimen holder that accommodates a stack of[unreadable] 10 bones, lumbar vertebrae or femora will be scanned to determine the individual volumetric densitometric[unreadable] contributions of cortical and cancellous bone. In addition, three-dimensional measurements of cortical and[unreadable] cancellous microarchitecture will be done. Aim 4. Provide murine bone mass determinations by dual-energy[unreadable] x-ray absorptiometry on Hologic or PIXImus instruments to meet the needs of the project leaders.[unreadable] Measurements of global, spinal, and femoral bone density will be performed serially, in longitudinal[unreadable] experiments, in live mice. Aim 5. Acquire biomechanical measurements of murine vertebral compression[unreadable] strength and femoral three-point bending using a material testing system to determine the significance of[unreadable] changes in bone mineral density and bone architecture. Aim 6. Train key personnel from the projects that[unreadable] need bone mass, biomechanical and histomorphometric measurements to help each team meet the goal of[unreadable] their projects. This centralized facility will provide for each of the projects a uniform and comprehensive[unreadable] investigation of the skeletal changes in bone mass, architecture, turnover and strength that occur with aging[unreadable] allowing determination of the efficacy of different treatment regimens in preventing fragility fractures.